The invention relates to conopeptides.
Cone snails (Conus) are widely dispersed marine gastropods that prey on fish, marine worms, and mollusks. Cone snails are venomous predators that elaborate peptide toxins in their venom ducts; the venom flows from the venom ducts through hollow stinging radular teeth, into the prey of the snails.
Several of these peptide toxins, generically referred to as conopeptides, have been characterized. The conotoxins are small peptides with a high density of disulfide bonds; cysteine residues can represent up to 50% of the amino acids in some conotoxins. Conotoxins target nicotinic acetylcholine receptors, sodium channels, and calcium channels, and thus behave as potent receptor antagonists.
Another group of peptide toxins includes the conantokins. These peptides, in contrast to other conotoxins, generally contain no cysteine residues. Conantokins are characterized by the presence of one or more .gamma.-carboxyglutamic acid (Gla) residue. Conantokin-G, isolated from the cone snail Conus geographus, has 17 residues, 5 of which are Gla residues; conantokin-T, isolated from Conus tulipa, has 21 residues, 4 of which are Gla residues. Many of the conantokins have N-methyl-D-aspartate (NMDA) antagonist activity.
Still other conopeptides have some of the characteristics of both the conotoxins and the conantokins. For example, the conopeptide Ctx TxVIIA, isolated from Conus textile, contains both Gla residues and cysteine residues.